A) and Active Set Methods
de Leeuw, Hornik, Mair
Journal of Statistical Software 2009

Correctness of Kruskal's algorithms for monotone regression with ties
de Leeuw, Psychometrica, 1977

Examples
--------
>>> from sklearn.datasets import make_regression
>>> from sklearn.isotonic import IsotonicRegression
>>> X, y = make_regression(n_samples=10, n_features=1, random_state=41)
>>> iso_reg = IsotonicRegression().fit(X, y)
>>> iso_reg.predict([.1, .2])
array([1.8628..., 3.7256...])
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